1. Field of the Invention
The present invention relates to an X-ray monochromator with simultaneous tuning of an asymmetric angle-and-radius of curvature, and more particularly relates to a single crystal X-ray monochromator which has a high focusing capability and a wide wavelength range from 1 .ANG. to 2 .ANG..
2. Related Art Statement
In these days, X-ray monochromators which are capable of selecting an arbitrary wavelength have become important due to the development of radiation light, and many developments for X-ray monochromators have been proposed. Recently a two-crystal monochromator and an asymmetric cut triangle monochromator (curved asymmetric triangle crystal spectroscopes) have been practically used. The two-crystal monochromator is remarkably convenient for use, because an exit X-ray direction is invariant for whichever wavelength. However, it has a disadvantage that the focusing capability is too low to exhibit the high intensity. Therefore, the asymmetric cut triangle bent monochromators have been used for many beamlines for protein crystallography which utilizes beamline BL6A from a bending electromagnet BL6A installed in the Photon Factory in Tsukuba, Ibaraki, Japan.
The asymmetric cut triangle bent monochromator has an advantage in realizing high intensity, with placed expectation for its application to various X-ray analyses. However, in this type of monochromators, the demagnification rate of a beam passing through the asymmetric cut crystal monochromator depends on the angle between the beam and the crystal surface with the asymmetry factor, which is then related to the wavelength. Therefore, the demagnification rate depends on the wavelength, and thus a usable wavelength range is narrow. For this reason, about ten kinds of different asymmetric cut crystals are required in order to generate X-rays of wavelengths ranging from 1 .ANG. to 2 .ANG.. In order to perform the beam demagnification and focusing over a wide range of wavelengths, several different asymmetric cut spectral crystals have to be prepared, and any desired one of them has to be used for respective wavelengths. Therefore, when a measurement using various wavelengths, e.g. a measurement using the abnormal dispersion effectively, is to be conducted, a very long time is required for replacing spectral crystals, and such a long time could not be practically accepted.
Further, the use of a strong X-ray source such as emitted light makes it difficult to cool the conventional asymmetric cut triangle monochromator, which unexpectedly provides a problem related to heat load. In particular, it is pointed out that the intensity of the emitted X-rays varies due to the heat load with the lapse of time, although the crystal does not melt due to the heat.